With the increased awareness that genetic mutation in somatic cells is associated with cancer, it would be extremely useful to have a method for monitoring genetic damage. Present methods, including the most commonly used, cytogenetic monitoring, are extemely laborious and have therefore not found wide application. Many of the methods available at present, such as the Ames test or the CHO tests of HLA mutation, test suspected mutagenic chemicals and do not provide in vivo monitoring. To address these limitations this proposal is directed toward developing a rapid direct method for detecting mutations in blood cells providing a possible assay for the screening of large numbers of individuals. The assay proposed here is based on enumerating cells bearing mutant HLA membrane antigens among peripheral blood lymphocytes. The mutations will be detected by a novel serological test which yields a positive signal by use of two selected monoclonal antibodies that react with independent regions of an HLA heavy chain. This positive signal will be the result of one of two proposed configurations in which the two antibodies will interact negatively with each other. A mutant at any single locus will be dominantly expressed with these assays and the presence of multiple HLA class I loci should increase the frequency of mutation at least four-fold compared to single allele systems. Preliminary work has resulted in acquisition of a series of HLA class I monomorphic antibodies which are being classified by addition and competition experiments. To test the feasibility of these assays, cells with mutations in HLA will be isolated to use in reconstruction experiments. If successful, this assay will represent an improved method for quantifying human genetic damage occuring in vivo. This is important for two reasons: 1) genetic damage increases the mutational load of the population resulting in higher levels of genetic disease and 2) mutagenesis correlates strongly with increased incidence of cancer. Our proposed test could be used in conjunction with a cell sorter as a screening method for identifying populations at increased risk for cancer with application in occupational and public health setting. Based on recent evidence of Fidler, mutation rates in individual tumors may also provide a prognostic indication of metastatic capacity.